When Harrison is first introduced, he's a 3 month old year baby that his father has been taking care of, alongside his job and "nightly activities". He experiences a regular lifestyle with his loving mother, Rita, and caring siblings, only to lose his mother to The Trinity Killer before he truly got to know her. Due to Rita's passing, Dexter had to hire a nanny to watch over his son so that he could both work and go out at late hours to track serial murderers. At first, he hires a woman named Sonya, then moving on to a more permanent nanny in Jamie Batista; Angel's younger sister, whom Harrison becomes emotionally attached to.

Throughout his aging, Harrison has known two of Dexter's girlfriends, following his mother's death. Firstly, he met Lumen Pierce, who nervously cared for him while with his father, and finally, Hannah McKay, whom he began to view as his own mother. After Dexter falls deeply in love with Hannah, Harrison too develops a strong bond with her and the three of them attempt to move to Argentina together, only for Dexter to not join them (due to having to fake his death). Currently, Harrison is living an open-ended life under Hannah's care.

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When first revealed in the first episode of Season 4, Harrison can be seen as a rather chunky child with a chubby face and light, partial hair on top of his head. His eyes are a deep blue at this age and he is portrayed by at least one child.

As of the second episode in Season 5, Harrison has changed drastically (even played by a different child) and shows a bright, smiling face with several teeth already in place. His hair has grown longer, but still hasn't grown out at this point. He sometimes has the facial expression that his own father, Dexter, has made popular...being that of a stern, non-smiling face when something is taken away from him (such an example being after he removes the head from a doll and Dexter puts the head back on, he kind of "glares" at Dexter for doing so). Since he is still just a child, he wears practically anything from a onesie to little shorts and shirts and of course, a (hopefully clean) diaper.

17 year old Harrison

While Dexter envisions his future with Hannah McKay and continuing his ways as a Serial Killer, he sees himself growing older with grey hair and his son having grown into an athletic young man with short blonde hair. This Harrison appears to be in his Junior or Senior year at high school, with a license to drive and an interest in basketball. Due to his attire (a pair of gym shorts, light hoodie and shirt) he appears to be part of his high school's basketball team and living a normal life. This is likely what Harrison would end up looking like, despite it only being a figment of Dexter's imagination.

Since Harrison, or "Dexter's Son", is only still a child, much of his personality consists of the typical behavior attributed to children - crying, sleeping, smiling, giggling, and fits of rage. Aside from these traits, he is just a baby whose presence is more important than his ability to demonstrate personality. However, during a therapy session (which may have been for comical relief), the therapist talks to Dexter about how Rita's death couldn't possibly have any negative effects to a child of his age...at which point Harrison pulls a head directly off a doll which kind of surprises both of them, especially Dexter (since he was "born" in his mother's blood as well). Dexter quickly goes over to reattach the head and as the therapist dismisses it as normal, Harrison gives a cold stare (similar to his father's on his targets) to Dexter as he returns to his seat, obviously not wanting him to mess with his "toy".

As the season progresses, more and more of Harrison's personality is being shown and is starting to worry Dexter. In the start of Episode 5, during a "Mommy and Me Class" with a bunch of other young children and their parents, Harrison cuts another young boy with his fingers in exactly the same spot that Dexter cuts his victims for the blood slides. And much to Dexter's surprise, Harrison has already wiped clean (most likely licked clean) the evidence of blood...though this may just be for comic relief at the moment, this may run-on through the season with more and more of Harrison's similarities to possibly becoming just like Dexter showing up quite clearly.

Near the start of the season, Rita informs Dexter that she is pregnant...which somewhat comes off as a shock to Dexter but at the same time, it hardly has time to affect him. Gradually they find out that the child will be a boy and Dexter starts to become attached to the child, wanting to pass on his "positive intentions" to the baby. The child plays a very symbolic role in this season, especially in the last episode as he indirectly helps Dexter (with the assistance of Harry) break free of his captor, kill him and escape to take care of his child...to live on and be there for his family.

Unlike most series which at least show the birth of a child, Harrison kind of pops up on you without much warning. At the very start of the episode when Dexter does his usual opening of "tonight's the night", the scene pans away to then show Harrison in his car-seat...having been driven around for a late night stroll. Harrison has apparently caused a lot of sleep disorder for Dexter, as a comical parody on the opening to the series is later shown the next morning.

Dexter comes home to find Harrison sitting in a pool of his mother's blood, just as Dexter once was.

For most of the season, Harrison is a background character that is more symbolic than actually being out there. He has the least screen time of the three children and is mainly used as a plot device to either return Dexter home during a hunt or provide a sense of humanity to his character. Eventually, however, the last episode starts off a trend that his father knows all too well...

Harrison is found sitting in a pool of blood after Dexter returns home from killing Trinity, crying loudly as his mother has been murdered (apparently by Trinity) and Dexter rushes down to him, instantly remembering images of his own past where his mother was killed and her blood drenched him. As Dexter closes Rita's eyes and carries Harrison out, many flashbacks occur simulating the similarities between both events.

The start of Season 5 picks up directly after the last episode of Season 4, in fact the same child is even used for this episode at relatively the same age which suggests that it was possibly filmed within close proximity of the previous episode (but released at a later time). Harrison is still in tears over his mother's death, though he probably doesn't understand exactly what's going on so that is what gets at him the most. As Dexter sits on the lawn, still in shock at what happened...a cop rudely tries to take the child from him until Dexter's sister, Debra Morgan, arrives and prevents the Officer from doing so.

Harrison is more prominent in this season, thus far having more screen time than even his two older siblings (who decided to live with their grandparents after the death of their mother, being too much to bare trying to live with Dexter...at least, that is what Astor felt). He has become heavily important to Dexter, who searched constantly (at least through 30 people) for a nanny to watch over him so that Dexter can somehow squeeze in time to kill a murderer or two. Eventually he finds a nanny that Harrison warms up to instantly, having no desire to stay with any of the previous candidates...she's the one.

During a therapy session regarding young Harrison's mental state and health, the therapist discloses to Dexter than at this age it is most likely impossible that it has affected him in any negative way...which is responded to with Harrison pulling the head off a doll. Dexter quickly reattaches it but Harrison glares at him for doing so, possibly suggesting that Harrison may be on a negative path...or at least creating somewhat of a comical situation. Later on when Dexter is busy hunting down Boyd Fowler, the nanny seems to have disappeared with Harrison after he returns home and assumes the worst...until she returns with Harrison in good health and eventually says she quits because she didn't see Dexter as a "responsible parent". Of course...Dexter is persistent and eventually gets her back, as she cannot resist taking care of little Harrison. By the end of the season, Harrison shows signs of having personality traits similar to his father indicating he might indeed be on a similar path like his father was. By the end of season 5, Harrison celebrates his 1st birthday with Dexter along with his family and friends.

Harrison goes to a Catholic Preschool for an interview in order to attend. Dexter butchers the interview by stating he believes in nothing. Later on Dexter convinces the Sister to take Harrison in saying Dexter wants him to have a normal childhood. At the end of episode one Dexter drops Harrison off at the preschool. Harrison then develops a stomach condition, and upon arrival at the hospital, it is determined that he has a ruptured appendix, and goes into surgery immediately. While waiting for news on the surgery Dexter asks for God's help and a sign that Harrison would be ok. Harrison survives the operation.

Travis threatens to kill Harrison if Dexter doesn't do as he says.

Harrison is later kidnapped by The Doomsday Killer, who was wearing the mask Dexter was wearing at the time as disguise, to be sacrificed as the final tableau. Luckily, Dexter intervenes and prevents Harrison from being killed by pretending to sacrifice himself instead.

Harrison makes few appearances in this season, as he was living with his half-brother and half-sister, Cody Morgan[1] and Astor Morgan.[2] (and Cody and Astor's grandparents...their father, Paul's mom and dad).

At the start of the season, Harrison has been aged a little bit. He now plays on a soccer team, takes swimming lessons, and talks a lot more. In the first episode of the season, Dexter takes Harrison along in his search for Deb. He briefly loses Harrison. One night, Dexter woke up to Harrison crying out 'Daddy.' He follows a trail of red, only to find Harrison on the cold tile floor, having consumed an entire box of red popsicles because he "loved them." Following the plot point of the episode, in which Dexter consumes everyone he loves, as does his son. Dexter then starts to feel guilty for bringing his son into his messed up life.

Harrison has shown an ability of lying easily when he was accused by Jamie of stealing the TV remote, to which he denies, but the remote was later found under his bed. During the series finale, Harrison is utterly abandoned by his father, who thought it necessary to move on in life (since he didn't want himself to affect Harrison) and so becomes a lumberjack in an unknown location, while entrusting Hannah with Harrison.

In the season 8 finale, Debra's former boss Elway is the ony person apart from Hannah and Dexter who knows that Harrison is with Hannah, as he has seen him with Hannah on the bus. Cody, Astor or Jamie the babysitter do not know Harrison's whereabouts. Dexter faked his own death, Harrison, however, simply has gone missing. The season 8 leaves a loose end as to whether Astor, Cody or Jamie will investigate Harrison's whereabouts, and whether Elway will inform the police that Harrison has been kidnapped by Hannah.

Although its unknown, it can be confirmed that Harrison was not negatively affected in any way by his mother's death, as he was too young to remember or have anything like such to affect him from that age.